The present invention relates to an electrical device, and in particular a switching and controlling device for a motor vehicle.
More particularly, it relates to such an electrical device which has a printed circuit foil carrying an electronic circuit and applied with its lower side on a heat conductive carrier plate and provided on its upper side with at least one heatable power component.
Such electrical devices are known in the art. One of such devices is disclosed, for example in the German document DE-PS 40 23 319. This electrical device has an electronic circuit with a base element and a printed board formed as a printed circuit foil and provided with conductor tracks or switching structures. A plurality of discrete components are connected with the printed circuit foil, and one or several components form so called power components which are heated during the operation of the circuit or the electrical device. The printed circuit foil is applied on a carrier plate which on the one hand mechanically stabilizes the printed circuit foil and on the other hand operates for heat withdrawal of heat generated by the power components. The carrier plate is composed for this purpose from a good heat conducting material, for mechanical materials such as aluminum or a similar material. Power elements in SMD-structure (SMD=Surface-Mounted-Device) must be applied in such electrical devices on the upper surface of the printed circuit foil facing away from the carrier plate. The heat transport from the power component to the heat conductive support plate must be performed therefore through the printed circuit foil. However, conventional printed circuit foils act in disadvantageous manner as heat insulators, since their heat conductivity is substantially lower than the heat conductivity of a (metallic) carrier plate. For improving the heat withdrawal from the SMD power element to the heat conductive support plate, it is known to provide the printed circuit foil under the applied power element with through contacts. Such through contacts are composed as a rule of openings extending through the printed circuit foil and having small diameter. On the upper side or on the lower side of the printed circuit foil they are surrounded by a substantially circular heat conductive coating, for example solder sheet, and the sheets on the upper side and the lower side are connected with one another in a heat conductive manner. The opening diameters of conventional through contacts is at most less than 1 mm. Due to the geometry of these through contacts in the construction having a plurality of the through contacts under a single power component, often an insufficient heat transmission from the power component to the carrier is obtained.